This is the first of two posts (in theory, I’ll remember to write the second) explaining why Jetpack is a big plugin with many features, rather than many individual plugins. This post will be looking at the primary technical reason. The abundance of other reasons will be in the subsequent post. (So please don’t read this post and think it’s the only reason — it’s not)

tl;dr: Dependency management sucks.

Jetpack, as you may be aware, is structured as a bunch of modules. Many — but not all — require a connection to WordPress.com to function. This isn’t for vanity purposes, it’s because they actually leverage the WordPress.com server infrastructure to do things harder, better, faster, stronger than a $5/month shared host is capable of. To do that, they need to be able to communicate securely with WordPress.com, and WordPress.com must be able to communicate securely back to your site.

Some of the modules that require a connection are things such as Publicize (which uses the WordPress.com API keys to publicize to assorted third-party systems, rather than making users register various developer accounts and get their own API keys), Related Posts (which syncs some content up to the WordPress.com servers and indexes it on a large ElasticSearch index more efficiently and accurately than could be done in a MySQL database), Monitor (which pings your site every five minutes and emails you if it’s down), Comments (which passes data back and forth behind the scenes to enable secure third-party comment authentication) — you get the idea.

We could bundle the connection library with each individual plugin. However, we’d need to make sure it was namespaced correctly so each different plugin can use its own correctly versioned instance of the connection classes. Which would then mean a user could have well over a dozen copies and different versions of the same connection class active at a given time. Which will make things more difficult with respect to developing the plugins, as you can’t assume methods in one are necessarily in another. And when you make a change in the master class, you need to scan each repository to make sure you’re not breaking anything there, and keep changes synced to well over a dozen repositories. But I digress.

To avoid duplicate code, the modules that depend on talking back and forth with WordPress.com all use a common library that handles signing and verifying requests, API calls, and the like.

Because it’s all packaged in a single plugin, we can be sure that it’s all running the required version. If Publicize needs a change in the core connection library, we can be sure that the version of the connection library in Jetpack has those changes. If the core connection library needs to change structure, we can make sure that any modules that used the old methods are updated to run the new ones instead. Everything is maintained so that it’s running smoothly and works properly with each other.

Now, if Likes, Single Sign On, After the Deadline, Post by Email and others were their own plugins, and connected to a separate Jetpack Core plugin, versioning gets tricky. It could work, in theory, if every plugin is kept up to date, always and forever. But the instant that the user is using, say, an outdated version of Subscriptions with an outdated Jetpack Core (which work perfectly together), and then installs the up-to-date WP.me Shortlinks plugin, things could break because WP.me Shortlinks expects a more up-to-date Jetpack Core. So you go ahead and update Jetpack Core to current, but now Subscriptions — which used to work perfectly — now breaks because there was a method change in Jetpack Core, that is fixed in the up-to-date version of Subscriptions, but the user isn’t running the up-to-date version. Horrible UX.

Plus, if the user doesn’t have any Jetpack stuff, the installation flow for their first Jetpack Plugin that needs the core would be something like this:

As I said, dependency management is hard, and there’s not really a good way to manage it in WordPress. There have been some very worthwhile attempts made, but none that can have a sufficiently solid user experience for an average user to compare with our current system and flow.

Any questions or suggestions about dependency management and Jetpack? Ask away!

So, why does Jetpack auto-activate features?

Well, to start off, I should probably clarify what we currently do on this. We don’t auto-activate every new module that comes in.

We never auto-activate features that affect the display or front-end of your site — or at least not unless a site administrator explicitly configures them to.

So, for example, something like Photon, which would swap all your content images to CDN-hosted versions, doesn’t auto-activate. Our comments system doesn’t auto-activate either, as that would swap out your native comment form. Our sharing buttons do, but they don’t display unless you take the time to drag down some sharing buttons to the output box under Settings > Sharing.

However, modules like Publicize, Widget Visibility, and the like — they just give you new tools that you can use, with no risk to affecting your everyday visitors. When users upgrade, we give them a notification of what just happened, and point out some new features we’ve built in that they may want to activate themselves.

One thing we’ve recently expanded on, perhaps six months ago, is a ‘plugin duplication list’, for lack of a better phrase. These aren’t plugins that have an actual code-based conflict with a module, they’re ones that may be … duplicating effort. Previously, we were just scanning for plugins that would output OG Meta Tags, and short-circuit our own provider. However, since Jetpack 2.6, which shipped in November 2013, we’re actually doing it via a filter for all modules. For example, if you’ve got Gravity Forms or Contact Form 7 installed and active, our internal Jetpack Contact Form won’t auto-activate. If you’ve got AddThis or ShareThis active, our sharing buttons module won’t even kick in.

Now, obviously, we can’t catch every single plugin that may be similar enough to one of our modules to give cause to negate auto-activation. So there’s a filter, `jetpack_get_default_modules`, that can be used in any plugin to cancel auto-activation on any module.

But I don’t like auto-activation of new features!

Okay.

You’re totally allowed not to.

We’re going to continue using our discretion to auto-activate select modules by default, but if you’d like to turn it off permanently for yours or a client’s site, we’ve made it ridiculously easy to do.

add_filter( 'jetpack_get_default_modules', '__return_empty_array' );

That’s it.

We believe that judiciously enabling new features is a win for users, especially considering 1) how low-impact most features are when ‘active’ but not actually implemented by a site owner, 2) how awkward it is for a site owner to have to enable something twice — for example, enabling the Custom Post Formats bit, and then having to visit Settings > Writing in order to actually enable the Portfolio custom post type.

If you have clients, that you’d like to be active in the relationship with, and customize the Jetpack experience for — that’s terrific. You’re the type of people that we add bunches of filters for. We’re all about empowering you to override our decisions, we just prefer to keep the default user interface free of a thousand toggles.